The present invention relates generally to optoelectronic devices, and more specifically to parallel optics assemblies for use in fiber optic communications.
The majority of computer and communication networks today rely on copper wiring to transmit data between nodes in the network. However, copper wiring has relatively limited bandwidth for carrying electrical signals which greatly constrains the amounts of data that it can be used to transmit. Many computer and communication networks, including a large part of the Internet, are now being built using fiber optic cabling which has superior bandwidth capabilities and can be used to transmit much greater amounts of data. With fiber optic cabling, data is transmitted using light signals (also called optical or photonic signals), rather than electrical signals. For example, a logical one may be represented by a light pulse of a specific duration and a logical zero may be represented by the absence of a light pulse for the same duration. In addition, it is also possible to transmit at the same time light at different wavelengths over a single strand of optic fiber, with each wavelength of light representing a distinct data stream. However, since computers use electrical signals as opposed to light signals the light signals used to transmit data over fiber optic links must be translated to electrical signals and vice-versa during the optical communication process. Building such fiber optic networks therefore requires optoelectronic transceivers (transmitters or receivers) which interface optical transmission mediums to electronic computing devices and transform optical signals to electronic signals and electronic signals to photonic signals.
Such optoelectronic transceivers may be provided using semiconductor devices (photoactive devices) such as photodiodes which act as photo-receivers or LEDs or laser diodes which act as photo-transmitters. While transceivers using such devices can provide satisfactory performance, the optical alignment of the photoactive devices with the ends of the thread-like fiber optic ends must be precise for an effective transfer of optical power. In parallel optics modules which use multiple fibers and multiple communications channels for high bandwidth applications the fiber optic ends are closely spaced in an array which greatly increases the complexity of this alignment task.
One past alignment technique for use in constructing parallel optics modules was to etch alignment grooves along the surface of a silicon substrate using photolithography techniques. These grooves were then used in precisely positioning the fibers and fiber optic ends in aligned relationships to edge-emitting laser diodes. Although this technique can accurately align the optical components, the arrays must be manually assembled. Consequently, the process is labor intensive and results in low yields due to assembly errors and quality assurance problems.
More recently some parallel optics modules have come to use metal lead frames for mounting the photoactive devices. The lead frames then have alignment holes that cooperate with guide pins for alignment purposes. The guide pins extend from the holes in the lead frame to corresponding holes in a ferrule supporting the optic fibers in order to provide for the alignment of the ferrule with the lead frame and the fibers with the photoactive devices. However, this type of design has weaknesses. The optoelectronic device must be very accurately mounted onto the metal lead flame and at the same time the alignment holes extending through the lead flame must be very accurately positioned. Should the optoelectronic device or alignment holes be misaligned, optical misalignment will occur even though the optical fibers may appear to be correctly aligned.
The present invention is directed to an optoelectronic subassembly for use as a transceiver in fiber optic communications systems where multiple parallel optical fibers are used in transmitting and receiving optical signals. The subassembly is adapted for mechanically and optically connecting with an optical ferrule and electrically connecting to a larger computing or communications system. The optical ferrule supports a set of optical communications fibers disposed in an array. The subassembly supports an optoelectronic device having a set of photoactive components also disposed in an array corresponding to the fiber array. The optoelectronic device is operative for either converting photonic signals to electrical signals (in a receiver) or electrical signals to photonic signals (in a transmitter). The optoelectronic subassembly includes a carrier which is precisely fabricated using photolithography techniques for aligning and supporting the optoelectronic device and photoactive components within it. The carrier further includes a precisely positioned alignment structure for cooperating with the optical ferrule to align the photoactive components of the optoelectronic device with the fibers in the ferrule when the two are connected together. Also, the carrier preferably includes a thin film layer and one or more alignment marks applied to the film layer which may be used for accurately mounting the optoelectronic device on the carrier. In the preferred embodiment the carrier includes a window section over which the film layer extends for allowing the optoelectronic device to be mounted on the rear face of the carrier with the photonic signals then passing through the window section to or from the back side of the carrier. The carrier itself is mounted in a frame section which is part of a larger carrier assembly including a multilayer circuit board, an edge connector and a flex circuit. The flex circuit runs throughout the carrier assembly forming part of the frame section and the circuit board. The carrier assembly provides structural support for the carrier and provides a large number of communications and control lines over which signals can be exchanged between devices on the carrier, the circuit board and with the edge connector.
In the preferred embodiment, the carrier primary comprises a silicon substrate which is fabricated from a silicon wafer. The silicon substrate carrier enables the use of photolithography techniques in the construction of precisely aligned features on the substrate such as alignment structures and marks. The use of a silicon substrate also enables the placement of electrical leads directly on the carrier to carry signals and power to the optoelectronic device containing the photoactive components and to other devices.
Also in accordance with the preferred embodiment, the film layer is composed of a dielectric material such silicon dioxide which is deposited on the silicon substrate using photolithography techniques. The alignment marks are similarly deposited with a high degree of accuracy on the film layer as metal traces. Additionally, a set of metallic traces may be placed on the film layer adjacent to the optical connection pathways between the photoactive components and the optical fibers in order to suppress EMI emissions.
Further in accordance with the preferred embodiment, the alignment structure includes a pair of alignment apertures extending through the carrier. A pair of guide pins are received in the alignment apertures and cooperate with the ferrule to align the optoelectronic device with the optical ferrule. A support block can also be used to provide support passages for receiving and supporting the far (distal) ends of the guide pins so that the guide pins and the carrier are supported, protected and maintained in accurate alignment.
In another aspect of the present invention, a method is provided for building an optoelectronic module for interconnecting optical fibers supported in an optical ferrule with photoactive components in an optoelectronic device. In a first step, a silicon substrate carrier is fabricated using photolithography techniques to have alignment marks for precisely mounting the optoelectronic device and include an alignment structure for use in aligning the carrier with the ferrule. In a second step, the optoelectronic device is precisely mounted onto the carrier using the alignment marks for positioning. In a third step, the optoelectronic module is assembled by engaging the alignment structure of the carrier with a corresponding alignment structure built into the optical ferrule thereby aligning the photoactive components with the optical fibers supported in the ferrule.
These and other features and advantages of the present invention will be presented in more detail in the following description of the invention and the accompanying figures that illustrate by way of example the principles of the invention.